High efficiency catalytic cracking stripping process

ABSTRACT

A catalytic cracking process operates with enhanced stripper efficiency by subjecting spent catalyst to microwave radiation before catalyst regeneration. Preferably the microwave frequency is one which ignores the catalytic cracking catalyst and preferentially excites the hydrocarbon or coke on the spent catalyst, the stripping steam conventionally used, or both the stripping steam and the hydrocarbonaceous coke. In preferred embodiments, microwave frequencies are used which are selective for various impurities in the coke, such as sulfur and/or nitrogen impurities. Additives, such as ferrous materials, may be added to augment the efficiency of desulfurization during stripping. The process is applicable to fluidized catalytic cracking and moving bed catalytic cracking units.

FIELD OF THE INVENTION

This invention relates to catalytic cracking of heavy hydrocarbon oilsto produce liquid hydrocarbons boiling in the gasoline and distillaterange. Microwave energy is used to aid in stripping of spent crackingcatalyst.

BACKGROUND OF THE INVENTION

The present invention can best be understood in the context of itscontribution to conventional FCC processes. Accordingly, a briefdiscussion of conventional cracking processes and catalysts follows.

Conversion of heavy petroleum fractions to lighter products by catalyticcracking is well known in the refining industry. Fluidized CatalyticCracking (FCC) is particularly advantageous for the purpose. The heavyfeed contacts hot regenerated catalyst and is cracked to lighterproducts. Carbonaceous deposits form on the catalyst, therebydeactivating it. The deactivated (spent) catalyst is separated fromcracked products, stripped of strippable hydrocarbons and conducted to aregenerator, where coke is burned off the catalyst with air, therebyregenerating the catalyst. The regenerated catalyst is then recycled tothe reactor. The reactor-regenerator assembly are usually maintained inheat balance. Heat generated by burning the coke in the regeneratorprovides sufficient thermal energy for catalytic cracking in thereactor. Control of reactor conversion is usually achieved bycontrolling the flow of hot regenerated catalyst to the reactor tomaintain a desired reactor temperature.

In most modern FCC units, the hot regenerated catalyst is added to thefeed at the base of a riser reactor. The fluidzation of the solidcatalyst particles may be promoted with a lift gas. Mixing andatomization of the feedstock may be promoted with steam, equal to 1-5wt. % of the hydrocarbon feed. Hot catalyst from the regenerator iscontacted with preheated (150°-375° C.) charge stock. The catalystvaporizes and heats the feed to the desired cracking temperature. Duringthe upward passage of the catalyst and feed, the feed is cracked, andcoke deposits on the catalyst. The coked catalyst and the crackedproducts exit the riser and enter a solid-gas separation system, e.g., aseries of cyclones, at the top of the reactor vessel. The crackedproducts pass to product separation. Typically, the cracked hydrocarbonproducts are fractionated into a series of products, including gas,gasoline, light gas oil, and heavy cycle gas oil. Some heavier thangasoline cycle oils may be recycled to the reactor. The bottoms product,a "slurry oil", may be allowed to settle. The catalyst rich solidsportions of the settled product may then be recycled to the reactor. Theclarified slurry oil is a heavy product.

The "reactor vessel" into which the riser discharges primarily separatescatalyst from cracked products, and permits catalyst stripping.

Older FCC units use some or all dense bed cracking. Down flow operationis also possible, in which case catalyst and oil are added to the top ofa vertical tube, or "downer," with cracked products removed from thebottom of the downer. Moving bed analogs of the FCC process, such asThermofor Catalytic Cracking (TCC) are also known.

Further details of FCC processes can be found in: U.S. Pat. Nos.3,152,065 (Sharp et al); 3,261,776 (Banman et al); 3,654,140 (Griffel etal); 3,812,029 (Snyder); 4,093,537, 4,118,337, 4,118,338, 4,218,306(Gross et al); 4,444,722 (Owen); 4,459,203 (Beech et al); 4,639,308(Lee); 4,675,099, 4,681,743 (Skraba) as well as in Venuto et al, FluidCatalytic Cracking With Zeolite Catalysts, Marcel Dekker, Inc. (1979).The entire contents of these patents and publication are incorporatedherein by reference.

Conventional FCC catalysts are usually finely divided acidic zeolites,preferably low coke-producing, high silica zeolite cracking catalystscomprising faujasite, rare earth Y (REY), dealuminized Y (DEALY),Ultrastable Y (USY), RE-USY, Ultrahydrophobic Y (UHP-Y) and other largepore zeolites.

Typically, FCC catalysts are fine particles having an average particlediameter of 20 to 100 microns, usually around 60-80 microns.

Catalyst for use in moving bed catalytic cracking units (TCC units) canbe in the form of spheres, pills, beads, or extrudates, and can have adiameter ranging from 1 to 6 mm.

Although the catalytic cracking process is highly efficient, and is thepreferred process in many refineries for converting heavier hydrocarbonsto lighter, more valuable products, there are still some areas whereimprovements are needed.

Catalyst stripping is one of these areas. After the catalytic crackingreaction is completed, the catalyst must be stripped of strippablehydrocarbons before being regenerated. The goal of this strippingoperation is to remove all strippable materials, leaving only coke.

In many catalytic cracking units, especially fluidized catalyticcracking units, much of the so called "coke" is actually valuablehydrocarbon product which is entrained, adsorbed, or otherwise presenton the spent catalyst. The same thing is true in moving bed catalyticcracking.

Many attempts have been made to improve the efficiency of catalyststripping. There is strong incentive for such improvements, becausebetter stripping will reduce emissions of sulfur and nitrogen compoundsfrom the regenerator, increase the recovery of valuable hydrocarbonproduct, unload the regenerator and reduce the amount of water ofcombustion formed in the regenerator. Each of these aspects will bediscussed below.

Sulfur and nitrogen emissions are limiting factors in many refineries.By this, it is meant that the refinery is operating at the upper limitpermitted by local regulations for emissions of SO_(x) and/or NO_(x)from the FCC flue gas. Sulfur emissions can be most easily controlled,and most expensively, by hydrotreating the feed to remove sulfurcompounds. Another alternative is running only sweet crudes, with alower sulfur content through the catalytic cracking unit. Anotherapproach is to add an SO_(x) acceptor material to the unit, whichreleases H₂ S in the catalytic cracking reactor side. Yet anotherapproach is conventional stack gas clean-up. Nitrogen oxides are asimilar problem, in that they represent a stack gas pollutant.Hydrotreating, a change in FCC or TCC regenerator operation, or going toa different crude which has less nitrogen in it, are all possiblemethods of controlling NO_(x) emissions. Some of these, e.g., adjustingthe regenerator operation so that a more reducing atmosphere is presenttherein, will reduce NO_(x) emissions but increase CO emissions.

Increased recovery of product is important because the cracked productsare extremely valuable, and they should not be merely burned, as asource of fuel in the refinery. Allowing potentially strippablehydrocarbons to enter the FCC or moving bed catalyst regeneration unitis equivalent to converting a valuable fuel oil fraction into a lowvalue coke product. This can cause "winding down" of the unit, whichreduces conversion.

Water of combustion is also a severe problem in catalytic crackingregenerators, because the hydrocarbons burn to form H₂ O and CO₂. Muchof the steam in the regenerator is the result of bad stripping. Steampartial pressures of 5-10 psia are a fact of life in many FCCregenerators. The H₂ O makes the FCC or TCC regenerator a catalyst"steamer", and this steaming leads to severe and rapid hydrothermaldeactivation of the high activity, zeolite based catalyst used in theseprocesses. The average effective life of zeolite based catalyst in manyFCC units is on the order of 5-15 days. Anything that can be done toreduce the steam partial pressure in the regenerator will result in asignificant increase in catalyst life.

Many catalytic cracking units are constrained solely by the capacity ofthe regenerator to burn off "coke" and create freshly regeneratedcatalyst. These units could be more efficiently run, and run at higherfeed rates, if less valuable hydrocarbon were being burned in theregenerator. Ideally, the catalytic cracking regenerator should removeonly catalytic coke, all other forms of coke either being removed or notcreated in the FCC reactor. This is the goal to which all refinersaspire, and yet in most regenerators only about 1/3-178 of the materialburned in the regenerator is catalytic coke. 1/2

Several attemps have been made to improve on stripping operations byincreasing either stripping time or temperature. A very promisingapproach is that taken in U.S. No. 4,481,103, Fluidized CatalyticCracking Process With Long Residence Time Steam Stripper, which isincorporated herein by reference. The only drawback to such an approachis that an additional vessel is required to achieve the long residencetime stripping, typically 1-5 minutes. Although this approacheffectively reduces the burning load on the regenerator, increasesrecovery of valuable products, and reduces sulfur emissions, thebenefits are not quite as great as desired. There is also a slightdisadvantage in that fairly long residence time of catalyst in thepresence of steam is required. At the relatively low temperaturesinvolved in U.S. No. 4,481,103, somewhat lower than the riser toptemperature, there is no significant catalyst deactivation, and catalystlife is probably improved overall, rather than reduced because of thestripping operation.

Another approach is high temperature stripping. It is known to operate astripping zone with some air or oxygen addition. The high temperaturestripping, with some combustion, will be highly effective at removingpotentially strippable hydrocarbons (by burning them!) and reducing theburning load in the regenerator, but there are several drawbacks. The"stripper" flue gas will be contaminated with significant amounts ofnitrogen (when air is used as the oxygen containing gas), carbonmonoxide, and SO_(x). There will be enough of these materials aroundthat the stripper effluent can no longer be mixed with the crackedproducts for production of more valuable hydrocarbons.

In U.S. Pat. No. 4,820,404, which is incorporated herein by reference, apreferred approach to high temperature stripping is disclosed. The spentcatalyst is mixed with some hot regenerated catalyst to form a hightemperature combined catalyst stream. This high temperature mixture canbe very effectively stripped with stripping steam. The stripper effluentcombines, as in the prior art stripping methods, with cracked vapors andthe combined hydrocarbon streams are sent to conventional productrecovery facilities. The stripped catalyst is then cooled andregenerated. This approach improves the efficiency of catalyststripping, because of the higher temperatures involved, but there aresome drawbacks. Operation with a stripper container, e.g., a 50/50 mixof spent catalyst and hot regenerated catalyst requires that thestripper handle twice the catalyst flow as it did previously. There is aminor amount of hydrothermal deactivation. Some hot regenerated catalystwill see a fairly severe steaming atmosphere in the stripper. The spentcatalyst will be subjected to steam stripping at a higher than normaltemperature. These are minor effects. Overall this process should extendcatalyst life as compared to conventional FCC units not using a hotstripper because the water precursors will be kept out of theregenerator.

A different approach, one focusing on the problem of increased SO_(x)emissions from the FCC regenerator, is disclosed in U.S. No. 4,267,072,which is incorporated herein by reference. In this patent a metallicreactant is added to the circulating FCC catalyst inventory. Themetallic reactant reacts with sulfur oxides in the regeneration zone andforms a stable metal- and sulfur containing compound. Thesesulfur-containing compounds are reported to break down tosulfur-containing gas which is withdrawn from the stripping zone.

We realized that none of the approaches discussed above could becompletely satisfactory. The long residence time approaches were notparticular for many units, which did not have the physical space to putin a long residence time stripper. High temperature stripping alsorequires significant unit modifications.

We realized that it was essential to make a radical departure from priorart FCC catalyst stripping procedures to achieve a significantimprovement in the stripping operation.

We realized that microwave energy could be used to make catalyststripping more efficient.

Candor compels mention of much prior work that has gone on the use ofmicrowave energy in hydrocarbon conversion. Ever since the work reportedin U.S. Pat. No. 3,503,865, which is incorporated herein by reference,researchers have known that microwave energy could be used toefficiently heat heavy, hydrocarbonaceous materials such as coal. InU.S. No. 3,503,865, coal was liquified using microwave energy.

Microwave radiation was used to enhance crystallization of zeolites inU.S. No. 4,778,666, Chu et al, which is incorporated herein byreference.

Attempts have been made to use microwave energy for in situ tar sands orheavy oil recovery projects. These uses of microwave energy have notbeen too successful. The material to be recovered (tar sands or heavyoil) was a relatively low value product. In-situ heating of it requiredthat 10 tons or rock, sand, etc. has to be heated to recover 1 ton oflow value material.

A much more efficient use of microwave energy for enhancement ofhydrocarbon conversion processes was reported in U.S. No. 4,545,879,which is incorporated herein by reference. This patent discloses atechnique for desulfurizing hydrocracked petroleum pitch containingorganic molecules having chemically bound sulfur. Particles of petroleumpitch and a para- or ferro magnetic material catalyst were intimatelymixed with the pitch, and the mixture subjected to microwave radiationin the presence of hydrogen to generate a high intensity oscillatingelectric field. This released at least part of the chemically boundsulfur from the pitch as sulfur-containing gases without substantialincrease of the temperature of the pitch. Use of microwave irradiation,gated in a train of short pulses, minimized heating of the pitch.

An invitation to use microwave energy in various petroleum refineryoperations is reported in U.S. No. 4,279,722, which is incorporatedherein by reference. This patent suggested that the catalytic crackingoperation would be improved by subjecting the feed and the crackingcatalyst to microwave energy. The patentee specified that the microwavesource is spaced in the riser cracker, and, " . . . where desirable, anadditional source which may be of a different frequency is placed in thereactor."

U.S. No. 4,144,189, which is incorporated herein by reference, taughtregenerating spent FCC catalyst in the presence of microwave energy. Thespent catalyst would be fluidized with hydrogen and microwaved toconvert the coke to volatile products which would be removed with thehydrogen, so that regenerated catalyst could be returned to the reactor.In an alternative embodiment, the patentee disclosed contacting thespent catalyst with a solvent then microwaving the solvent/catalystslurry to regenerate the catalyst.

U.S. No. 4,076,607, which is incorporated herein by reference, disclosesa process for coal desulfurization generating extremely low amounts ofheat. The patentee taught use of microwave energy to introducethermochemical, in-situ reactions to liberate sulfur in the form ofstable gaseous species, such as H₂ S, COS and SO₂.

None of the prior workers in the microwave field address the problems ofimproving the operation of the FCC stripper in a practical manner. Mostof the microwave processes make poor use of an expensive energy source.This can be better understood by considering what goes on in an FCC.

Operation of a catalytic cracking unit using microwave energy to, e.g.,activate a mixture of fresh feed and catalytic cracking catalyst wouldrequire enormous amounts of microwave energy. In FCC units there areusually 3-10 weights of catalyst per weight of oil. A large FCC unitmight be a 50,000 BPD unit. The amount of energy needed to microwave50,000 BPD of oil plus perhaps 5 times the weight of this oil in hotcatalyst is enormous. The improvements expected in the catalyst crackingoperation are not sufficient, it is believed, to justify such anexpense.

Use of microwave energy to regenerate spent catalytic cracking catalystcould result in extremely high energy cost. Quite a lot of hydrogenwould be required to gasify coke back to hydrocarbons in a hydrogen fed,microwave irradiated FCC regenerator. The catalyst resulting from such aregeneration would not be an especially high temperature, so some othersource of heat would be needed to supply the endothermic heat of thecatalytic cracking reaction. Regeneration of FCC catalyst by contactwith a solvent also would require an enormous expenditure of energy, andwould not produce the hot regenerated catalyst necessary to supply theheat needed for the cracking reaction.

We realized that modern FCC units operate fairly efficiently in both theriser reactor and in the regenerator. By this we do not mean that allthings are perfect, but that only minor improvements in the operation ofthe riser reactor or the FCC regenerator are all that can be hoped forin such a mature process. The only area in catalytic cracking wheregross inefficiences remain is the catalyst stripper. FCC operators haveknown that 1/3-1/2 of the so called "coke" remaining on catalyst fed tothe regenerator is actually the product of an inefficient strippingoperation.

We have now discovered a way to profoundly improve the operation of theFCC catalyst stripper.

BRIEF SUMMARY OF THE INVENTION

Accordingly, the present invention provides in a process for thecatalytic cracking of a heavy, hydrocarbonaceous feed to lightercomponents by contact of the feed with a source of hot regeneratedcatalyst to form a mixture of spent catalyst and cracked products whichmixture is separated into a cracked products rich vapor phase and aspent catalyst phase, the spent catalyst is stripped in a catalyststripper to remove strippable materials and produce stripped catalystcomprising coke and unstripped hydrocarbons, and the stripped catalystis then regenerated with an oxygen-containing gas to produce hotregenerated catalyst which is recycled to contact fresh feed, theimprovement comprising microwave radiation treatment of spent catalystafter separation of spent catalyst from cracked products and beforeregeneration of the catalyst.

In another embodiment the present invention provides an apparatus forthe catalytic cracking of a heavy, hydrocarbonaceous feed to lightercomponents by contact of the feed with a source of hot regeneratedcatalyst to form a mixture of spent catalyst and cracked products whichmixture is separated into a cracked products rich vapor phase and aspent catalyst phase, the spent catalyst is stripped in a catalyststripper to remove strippable materials and produce stripped catalystcomprising coke and unstripped hydrocarbons, and the stripped catalystis then regenerated with an oxygen-containing gas to produce hotregenerated catalyst which is recycled to contact fresh feed,characterized by a catalyst stripper having operatively associatedtherewith a means for generating microwave radiation and a means fordistributing said radiation into said stripper.

DETAILED DESCRIPTION Brief Description of the Drawings

FIG. 1 is a simplified schematic view of one embodiment of the presentinvention, an exemplary FCC unit with a microwave heater about thecatalyst stripper.

FIG. 2 shows the effect of stripping temperature/residence time oncatalyst coke.

FIG. 3 shows the effect of stripping time/temperature on sulfur.

FIG. 4 shows the effect of microwave heating times on water, FCCcatalyst and peanut oil.

FIG. 1, is a schematic flow diagram of an exemplary FCC unit. Feed fromline 2 is charged to the bottom of the riser reactor 4. Hot regeneratedcatalyst is added via conduit 5, equipped with a flow control valve. Alift gas may be introduced near the liquid and solid feed inlets bymeans not shown. The riser reactor is an elongated, cylindricalsmooth-walled tube.

The feed vaporizes and forms a dilute phase suspension with the FCCcatalyst. The suspension passes up the riser, which generally gets widerto accomodate volumetric expansion. Cracked products and coked catalystmay pass into a solid-vapor separation means, such as a conventionalcyclone. Preferably, the riser has a deflector and short residence timestripper, as disclosed in U.S. No. 4,269,552 (Haddad and Owen) which isincorporated by reference. Another good design is the closed cyclonedesign disclosed in U.S. No. 4,749,471 (Kam et al) which is incorporatedby reference. A means for stripping entrained hydrocarbons from thecatalyst is provided in stripper 13. Preferably some conventionalstripping steam is added via line 41. The microwave stripping sectionshown in the figure is a simle implementation of the present invention,the incorporation of multiple microwave sources 100, 102 radiallydisposed about the stripping section. The stripping section ispreferably lined with a material which reflects the selected microwaveradiation, to ensure that the microwave energy is consumed in heating uphydrocarbons, and sulfur and nitrogen compounds, and not wasted inheating up the steel stripper vessel. Multiple elevations of microwavesources are shown, to allow for some fine tuning of the process. It maybe most beneficial to provide most of the microwave energy in arelatively dense phase region of the stripper, which permits a longerresidence time. It may, for some crude sources, be optimum to providemore of the microwave stripping via source 102 in a higher portion ofthe stripper, even up into the dilute phase portion thereof, because anygas released from such portions can be promptly recovered as crackedproduct, and will not tend to be entrained with stripped catalyst intothe regenerator.

Although the embodiment shown in the drawing will be the optimuminstallation in many commercial units, it should not be consideredlimiting. In new units, the use of a multi-stage microwave stripper,with the ability to remove stripped products as multiple points in thestripping operation, is highly preferred. With the ability toselectively heat hydrocarbons, and/or sulfur and nitrogen compoundsafforded by the present invention, use of extremely short residence timestripping is now possible. Stripping techniques heretofore used tode-water paper pulp are now applicable to catalytic stripping processes.By this is meant that the catalyst, after microwaving, could be passedover relatively large cross-sectional area surfaces with a vacuum on oneside of the surface to aid in stripping operation. Porous stainlesssteel filters can be used. In another embodiment, annular flow ofcatalyst around a porous stainless steel filter can be used to striphydrocarbons and/or sulfur and nitrogen compounds from catalyst whichhas been microwaved.

Cracked products and stripper effluent vapors are combined and withdrawnfrom the reactor by conduit 12.

Stripped catalyst containing coke is withdrawn via conduit 7 and chargedto conventional regenerator 6. The catalyst is regenerated by contactwith an oxygen-containing gas, usually air added via line 25. Flue gasis withdrawn from the regenerator by line 10. Catalyst circulates fromcoke combustor 17 to second dense bed 21. Some catalyst is recycled tothe base 11 of coke combustor via line 15.

Conditions in the cracking reactor can be conventional. Usually theheavy feed will be preheated to about 150° C. to 375° C. The regeneratoroperates at about 650° C. to 750° C. and the catalyst to feed weightratio is usually about 4:1 to 8:1, adjusted as necessary to hold adesired reactor outlet usually about 450° C. to 550° C.

Cracked product from the FCC unit passes via line 12 to mainfractionator 30, where product is separated into a heavy, slurry oilstream 35, heavy cycle oil 34 light cycle oil 33 naphtha 32, and a lightoverhead stream 31, rich in C₂ -C₄ olefins, C₁ -C₄ saturates, and otherlight cracked gas components. This light stream is usually treated in anunsaturated gas plant to recover various light gas streams, including C₃-C₄ LPG, and optionally C₂ -fuel gas or the like.

The improved stripper of the present invention works very well withconventional FCC units and in TCC units. The maximum benefit from thepresent invention will frequently be achieved when a heavy, metalscontaining residual feed is at least part of the feed to the catalyticcracking unit.

FEEDS

The feed can include any conventional feed for catalytic cracking units.Preferably the feed comprises a wholly or partly non-distillablefraction, e.g., 650° C.+boiling range material.

Conventional cracking feeds, such as gas oil, vacuum gas oil, wholecrudes, etc. can also be used. Because of the more efficient strippingdesign of the present invention, there will be excess capacity in theregenerator, so the FCC unit can tolerate significantly higherconversions, or as is more likely to be the case, significantly higherlevels of heavy, non-distillable, residual feeds. Other heavy feedswhich may be present include coal liquids, tar sands, shale oils, andsimilar heavy feeds which have a tendency to produce a lot of coke onconventional catalytic cracking catalyst.

FCC PROCESS

The fluidized catalytic cracking process, in the reactor section andregenerator section, are conventional. They will operate moreefficiently, because of the improvements afforded in their operation byuse of the inventive stripper design.

The FCC regenerator can be operated conventionally. Because of thesignificantly reduced burning load which is a by product of the betterstripping operation, more catalyst can be regenerated, or moreimportantly, more or more refractive hydrocarbon can be cracked.

The FCC catalyst is conventional, typically a large pore zeolite in amatrix. The large-pore zeolite cracking component may be conventional.Some of these zeolites, and patents describing their preparation arediscussed hereinafter. Zeolite X, zeolite Y, and higher silica forms ofzeolite Y such as dealuminized Y (DEAL; U.S. Pat. No. 3,442,795; U.S.Pat. No. 4,331,694 and U.S. Pat. No. 4,401,556), ultra stable Y (US Y;U.S. Pat. No. 3,449,070), ultrahydrophobic Y (UHP Y, U.S. Pat. No.4,401,556) and similar materials may be used herein. These materials maybe subjected to conventional treatments, such as impregnation or ionexchange with rare earths to increase stability. These patents areincorporated herein by reference.

The large-pore zeolite should have a pore opening of at least about 7angstroms. This zeolite does most of the cracking of large molecules inthe feed. Preferably, conventional FCC catalyst, e.g., REY or RE-USY, ina silica-alumina-clay matrix is used.

Very large pore materials, such as VPI-5 or pillared clays such asdisclosed in U.S. Pat. No. 4,742,033, which is incorporated byreference, may be used as part or all of the "large-pore" zeolite.

The catalyst may also contain other shape selective zeolites, in thesame particle, or the shape selective zeolites may be in separateparticles.

Any shape selective zeolite which at the conditions experienced in acatalytic cracking unit promotes formation of olefinic materials, orpromotes paraffin aromatization, can be used. Any zeolite having aconstraint index of 1-12 can be used herein. Details of the ConstraintIndex test procedures are provided in J. Catalysis 67, 218-222 (1981)and in U.S. Pat. No. 4,711,710 (Chen et al), both of which areincorporated herein by reference.

Preferred shape selective zeolites are exemplified by ZSM-5, ZSM-11,ZSM-12, ZSM-23, ZSM-35, ZSM-38, ZSM-48, ZSM-57 and similar materials.

ZSM-5 is described in U.S. No. 3,702,886, U.S. Reissue 29,948 and inU.S. Pat. No. 4,061,724 (describing a high silica ZSM-5 as"silicalite").

ZSM-11 is described in U.S. Pat. No. 3,709,979.

ZSM-12 is described in U.S. Pat. No. 3,832,449.

ZSM-23 is described in U.S. Pat. No. 4,076,842.

ZSM-35 is described in U.S. Pat. No. 4,016,245.

ZSM-57 is described in U.S. Pat. No. 4,046,859.

These patents are incorporated herein by reference.

Zeolites in which some other framework element is present in partial ortotal substitution of aluminum can be advantageous. Elements which canbe substituted for part or all of the framework aluminum are boron andother metals which are heavier than aluminum, e.g., gallium, zirconiumand titanium. Specific examples of such catalysts include ZSM-5 orzeolite beta containing boron, gallium, zirconium and/or titanium. Inlieu of, or in addition to, being incorporated into the zeoliteframework, these and other catalytically active elements can also bedeposited upon the zeolite by any suitable procedure, e.g.,impregnation.

Preferably relatively high silica shape selective zeolites are used,i.e., with a silica/alumina ratio above 20/1, and more preferably with aratio of 70/1, 100/1, 500/1 or even higher.

MICROWAVE AUGMENTED CATALYST STRIPPING

The present invention may be implemented using multiple modes ofmicrowave augmented catalyst stripping. The choice as to the precisemethod of implementation at a given refinery will be based on many localconstraints, such as size, capital constraints, and the amount ofstripping and/or sulfur removal required to meet local air pollutionregulations.

The frequency range of microwave energy used can range from about 600 to50,000 MHZ, preferably about 900 to 30,000 more preferably about 900 to3,600 MHZ and most preferably about 915 to about 2450 MHZ. The frequencychosen depends to some extent on the goal, i.e., gross heating orpromotion of a selected reaction.

The different phases of implementation are discussed below.

Phase I--Hot Stripping

Phase II--Tuned Stripping-Catalyst Transparent

Phase III--Tuned Stripping-Hydrocarbon Selective

Phase IV--Tuned Stripping-S, N Selective

Phase V--Tuned Stripping With Additive

PHASE I--HOT STRIPPING

At its simplest, the present invention may simply use the microwavesource as a way of heating up the catalyst to be stripped. Thismicrowave treatment can be used in conjunction with conventional steamstripping of spent catalyst to result in a somewhat hotter strippingoperation. The microwaves merely heat up the entire mixture of strippinggas and spent catalyst, either before or after a conventional strippingoperation.

PHASE II--CATALYST TRANSPARENT

Preferably, the microwaves are tuned so that a selective heating isachieved, i.e., the microwave frequency chosen does not preferentiallyheat the conventional catalytic cracking catalyst. The common microwavesources used for household and industrial microwave ovens are tunedprimarily to heat up water molecules, and such microwave frequencies doa reasonably good job of heating hydrocarbons and water.

Household type microwave generators are a readily available, low costsource of microwave energy. Although they are somewhat tuned to excitewater vapor molecules, they are efficient for use herein because of theconditions which exist in the catalyst stripper of fluidized catalyticcracking units. The material in the stripper is essentially allcatalyst, with 1-2 wt.% coke and unstripped hydrocarbons, and a modestamount of stripping steam, perhaps up to 5 wt. % steam.

Although FCC catalysts contain quite a lot of metal, typically severalwt. % rare earth metals, along with nickel, vanadium, and iron which aredeposited on the catalyst due to contamination of the feed, thesemetal-containing catalysts are largely transparent to householdmicrowave sources. This means that the bulk of the microwave energy canbe expended on heating up stripping steam and the 1-2 parts ofhydrocarbon per 100 parts of coke plus unstripped hydrocarbons, withsome of the energy being spent on the stripping steam. This means thatmicrowave treating of the catalyst stripper is at least 1, and up to 2orders of magnitude more efficient in its use of microwave energy thane.g., microwave processing of the FCC feed.

PHASE III--HYDROCARBON SELECTIVE

Preferably, the microwave source used is one which selectively heatshydrocarbons, and heats neither equilibrium catalytic cracking catalystnor water.

PHASE IV--TUNED FOR S, N

In a preferred implementation of the present invention, the microwavesource is selected to have a frequency, or frequencies, which promoteselective reactions. The microwave frequency can be selected to excitesulfur-carbon bonds and/or excite nitrogen-carbon bonds, and promoteremoval of sulfur and nitrogen compounds from the coke and unstrippedhydrocarbons on the spent catalyst. This permits another significantincrease in the efficiency of the use of the microwave energy. It is nolonger necessary to heat or excite the catalyst, the bulk of the cokeand unstripped hydrocarbons, nor the steam. The specific molecular bondssought to be stripped, such as sulfur and nitrogen, are targeted by themicrowave source. This will slightly reduce the amount of hydrocarbonthat is burned in the regenerator, but greatly reduce SOx and/or NOxemissions.

PHASE V--ADDITIVES

It is also possible, and will be preferred in some instances, to operatewith additives which have catalytic and/or physical properties whichmake efficacious use of a microwave energy source. A source of ironfilings, having a particle size distribution compatible with that of theFCC catalyst may be used, or extremely fine particles of iron filings,in the 5-10 micron range, may be used to permit more selective heatingof desired surface sites and promote the catalytic removal of a desiredcompound, e.g., sulfur compounds. Use of 5-10 micron particles of ironmight seem to be too small to permit continued use in an FCC unit,because most catalyst particles are in the range of 20-100 microns, butparticles of this size are attracted to the conventional FCC catalyst byelectrostatic attraction. Only minor amounts of such materials areneeded in the present invention, so their continual addition, and lossfrom the unit, can be tolerated in view of the enhanced sulfur removalthat can be achieved with the use of such additives. The fine additivescan also be recovered from downstream processing steps, and recycled tothe FCC unit, if desired.

MODIFICATIONS TO FCC STRIPPER

Although most efficient operation could be achieved by completelyredesigning the stripper, and providing a reduced residence time, withmore stages of vapor separation, the process of the present inventioncan be implemented in existing FCC strippers. The microwaves can begenerated at or near the FCC stripper, and directed to the stripper viaconventional wage guide tubes. It will be necessary to provide ports oropenings in the catalyst stripper for admission of microwave energy.Although the temperatures here are fairly high, typically 800°-950° F.,the pressures are fairly low, usually ranging from atmospheric to 2-3atmospheres.

Microwaves may be added from radially out to in, in to out, or somecombination of both. Many FCC strippers have elaborate steamdistribution systems for steam stripping and these may be wholly orpartly replaced with a microwave distribution system.

The microwave stripper may also be implemented in the dilute phase justabove the dense bed of the catalyst stripper. This is a very good placeto irradiate the spent catalyst, because the vaporized hydrocarbons fromthe catalyst will not have to travel far to exit the stripper. This is abetter place to remove the stripped hydrocarbons, than, e.g., the baseof the catalyst stripper where hydrocarbons released from the bottom ofthe stripper may well become entrained again by incoming spent catalystadded to the top of the stripper.

The most effective implementation of the present invention will be inconjunction with a riser reactor which quickly separates catalyst fromcracked products. Microwaving the spent catalyst immediately after suchseparation will minimize re-entrainment of stripped hydrocarbons, andpermit multi-stage stripping of catalyst. This means that microwavestripping of catalyst discharged from, e.g., a riser cyclone, can besupplemented with conventional steam stripping of the catalyst in theFCC unit.

In the most efficient embodiment, a riser cyclone stripping zone, withsteam stripping, is followed by a microwave stripping zone, which may ormay not be followed by a conventional catalyst stripper. A microwaveenhanced stripping cyclone may also be used.

MOVING BED CATALYTIC CRACKING

A microwave heating section may be added just before, just after, orcoextensive with the steam stripping section now used in moving bedunits.

Moving bed units are harder to modify than FCC units because there is noeasy way to provide an additional, separate stripping section betweenthe reactor and the regenerator.

EXPERIMENTAL EXAMPLE 1 (PRIOR ART)

Example 1 is represented by FIGS. 2 and 3 which show the effect of timeand temperature on the carbon and sulfur content in conventionalcatalyst stripping.

FIG. 2 shows the effect of stripping time and temperature on catalystcoke. The pilot plant unit used to generate the data did not have amicrowave source, it was a conventional pilot plant stripping apparatus.The pilot plant stripper was designed to simulate to the extent possiblewhat occurs in commercial FCC units. Obviously, commercial FCC units donot operate at the extreme temperatures reported, up to 1500° F., inFIG. 2. It is easy to achieve such temperatures in a pilot plant unit,but not practical in commercial catalytic cracking operations.

FIG. 3 is a similar plot, but this time the effect of strippingtemperature/residence time on catalyst sulfur is shown. In general, anincrease in either time or temperature reduces the sulfur level on thespent catalyst.

FIGS. 2 and 3 both show the importance of better stripping operation onreducing the amount of combustible material charged to a typicalregenerator, and on reducing sulfur pollution generated in theregenerator. The figures also demonstrate just how much improvement ispossible in conventional stripping operation. In a typical commercialunit, 15-20% of the material on the spent catalyst is actually astrippable hydrocarbon. This means that conventional FCC regeneratorsburn much more than they have to in order to remove catalytic coke fromthe catalyst.

EXAMPLE 2 (INVENTION)

Example 2 shows on implementation of the present invention, the Phase IIimplementation using a microwave source which largely ignores theconventional FCC catalyst.

A conventional FCC catalyst, GXO-41+, was used for the experiments. Thephysical properties are reported below.

    ______________________________________                                        GXO-41+ Equilibrium Catalyst                                                  ______________________________________                                        Surface Area, m.sup.2 /g 100                                                  Pore Volume, cc/g        .30                                                  Avg Bulk Density, g/cc   .82                                                  Particle Size                                                                 0-40 microns             8%                                                   0-80 microns             88%                                                  Avg. Part. size          61                                                   ______________________________________                                    

This catalyst was a commercial equilibrium catalyst, primarily GXO-41+,and contained all the metals contamination, rare earth metals, etc.,associated with commercial FCC catalysts. A commercial, equilibriumsample of FCC catalyst was used because only such samples can be trulyrepresentative of the types of catalyst to be encountered in commercialpractice.

80 cc samples of all of the materials, i.e., water, peanut oil, andequilibrium catalyst, were placed in a conventional, commercial (J. C.Penney) 500 watt microwave oven. Temperatures were measured every 15seconds, and the results plotted, as shown in FIG. 4.

The results show that the commercial FCC equilibrium catalyst waslargely ignored by the microwaves. Peanut oil, which would have heatingcharacteristics similar to those of heavy hydrocarbons, waspreferentially heated by the microwaves. Water was very efficientlyheated by the microwave source, but this was to be expected ascommercial microwave ovens are tuned to excite water molecules.

"WINDING-UP"

Optimizing stripper efficiency by use of microwave energy not onlyreduces the amount of hydrocarbon (HC) burned in the regenerator, butalso lowers the regenerator temperature. This allows a refiner to`wind-up` the unit and increase cat/oil ratios and realize theassociated conversion benefits. For a given riser top temperature,catalyst circulation (and catalyst/oil ratio) is increased with improvedstripping. This `winding-up` of the unit results in increased conversionas shown below.

    ______________________________________                                        Unstripped                                                                    HC's/Total Coke                                                                           Conversion to 385° F.                                                                  Gasoline Yield                                    ______________________________________                                        15%         BASE            BASE                                              10%         +1.4 Vol %      +1.1 Vol %                                         5%         +2.9 Vol %      +2.1 Vol %                                         0%         +4.3 Vol %      +3.1 Vol %                                        ______________________________________                                    

For a regenerator-limited operation, the process of the presentinvention also permits increased amounts of poor quality feedstocks,such as resids to be processed.

Reduction of SO_(x) emissions from the regenerator is becomingincreasingly important as evironmental regulations become morestringent. Microwave stripping can significantly reduce SO_(x)emissions.

Catalyst activity will be enhanced by the practice of the presentinvention, because much of the hydrogen contained in the hydrocarbons in"coke" is removed by the microwave stripping process of the presentinvention. This will reduce the amount of "water of combustion" formedin the FCC regenerator, and reduce catalyst steaming (and deactivation)in the regenerator.

We claim:
 1. In a process for the catalytic cracking of a heavy,hydrocarbonaceous feed to lighter components by contact of the feed witha source of hot regenerated catalyst to form a mixture of spent catalystand cracked products which mixture is separated into a cracked productsrich vapor phase and a spent catalyst phase, the spent catalyst isstripped in a catalyst stripper to remove strippable materials andproduce stripped catalyst comprising coke and unstripped hydrocarbons,and the stripped catalyst is then regenerated with an oxygen-containinggas to produce hot regeneated catalyst which is recycled to contactfresh feed, the improvement comprising subjecting said spent catalyst tomicrowave radiation treatment after separation of said spent catalystfrom cracked products and before regeneration of the catalyst.
 2. Theimproved process of claim 1 wherein the catalytic cracking process is afluidized catalytic cracking process.
 3. The improved process of claim 1wherein the catalytic cracking process is a moving bed catalyticcracking process.
 4. The improved process of claim 1 wherein themicrowave radiation is emitted at a frequency which preferentially heatsup unstripped hydrocarbon and coke faster than catalytic crackingcatalyst.
 5. The improved process of claim 1 wherein the microwaveradiation is in the frequency range of 900 to 3,600 MHZ.
 6. The improvedprocess of claim 1 wherein the microwave radiation selectively heatshydrocarbons.
 7. The improved process of claim 1 wherein the microwaveradiation selectively excites sulfur, sulfur compounds or mixturesthereof.
 8. The improved process of claim 1 wherein the microwaveradiation selectively excites nitrogen compounds.
 9. The improvedprocess of claim 1 wherein the heavy feed contains sulfur, the strippedcatalyst contains sulfur, and the catalytic cracking catalyst comprisesat least one additive which, in the presence of microwave radiation,acts as a desulfurization catalyst in the catalyst stripper and producesa stripped catalyst having a reduced sulfur content in the coke relativeto the sulfur content of the coke before microwave radiation treatment.10. The improved process of claim 9 wherein the additive comprises iron.11. The improved process of claim 1 wherein the microwave radiation isemitted at a frequency which preferentially superheats the strippingsteam faster than the catalytic cracking catalyst.
 12. The improvedprocess of claim 1 wherein stripped hydrocarbons, sulfur compounds,nitrogen compounds or mixtures thereof are removed from at least twoelevations along said stripper.